1. Field of the Invention
Example embodiments of the present invention relate to a semiconductor device including a fuse coupled with a redundancy circuit, a fabrication method thereof and a laser repair method for a semiconductor device using fuse cutting. More particularly, example embodiments of the present invention relate to a semiconductor device including a fuse focus detector for determining a focus offset value of a laser beam used for laser cutting, a semiconductor device fabrication method and a laser repair method using the fuse focus detector.
2. Description of the Related Art
As semiconductor devices are becoming highly integrated and a capacitance level thereof is also being increased, memory cells are more likely to have defects resulting from the fabrication of the semiconductor devices. As a result, a product yield of a semiconductor device may be reduced. One representative attempt to overcome the reduction in the product yield is to use a redundancy circuit to replace a defective main cell of a semiconductor memory device. Generally, a redundancy circuit replaces a defective main cell by cutting a corresponding fuse within a fuse box formed in a peripheral region of a semiconductor memory device. The fuse may be cut during the performance of a laser repair method. The laser repair method may include selectively cutting a fuse within a fuse box based on test results from a test performed on the semiconductor device.
During a laser repair method for replacing a defective cell with a normal redundancy circuit, a laser beam having a certain spot size may be used for fuse cutting. As the integration scale of semiconductor devices has become highly advanced, a fuse size and a pitch between the fuses have also become smaller. When such micronized fuses are cut, the spot size of a laser beam used for the fuse cutting and the thickness of a fuse may be important factors. However, when an etching process is performed to open the fuses during a method of fabricating a semiconductor device, the fuses may be exposed and may have varying thickness from the top. The thickness of each of the fuses may be different from each other depending on a position of the fuses on a wafer. Therefore, it may be difficult to control the uniformity of the final thicknesses of the fuses in different regions of the wafer.
Because of a variation in fuse thickness, which may depend on a position on a wafer, a focus offset value indicating a distance between a focused point and a lens through which a laser beam is emitted should be varied depending on a position on a wafer. However, in conventional fuse cutting methods and technology, a consistent focus offset value is applied regardless of the position on the wafer. As a result, fuses adjacent to a target fuse to be cut may be damaged and/or the target fuse may not be cut. Also, because a difference between focus offset values of a central region and an edge region may be large, a number of chips on a wafer may be severely affected and/or become defective.